igneous
Basalt River Pebble
Aphanitic Mafic Igneous Rock
Hardness: 5-6 Mohs. Color: Dark grey to black with possible green olivine specks. Luster: Dull/earthy. Crystal structure: Microcrystalline (aphanitic). Specific Gravity: 2.8-3.0.
- Hardness
- 5-6 Mohs
- Color
- Dark grey to black with possible green olivine specks
- Luster
- Dull/earthy
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Physical properties
Hardness: 5-6 Mohs. Color: Dark grey to black with possible green olivine specks. Luster: Dull/earthy. Crystal structure: Microcrystalline (aphanitic). Specific Gravity: 2.8-3.0.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. This specimen has been rounded and smoothed by water erosion in a river or coastal environment.
Uses & applications
Commonly used as aggregate in construction, road base, and high-quality specimens are used in aquarium landscaping or as river stones for massage therapy.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also found on the Moon and Mars.
Field identification & locations
Identified by its dark color, heavy feel for its size (high density), and lack of visible large crystals. Commonly found in volcanic regions or riverbeds downstream from volcanic sources.
